Sintered binding agent of the portland cement type and process for manufacturing same



Patented June 18, 1940 UNITED STATES PATENT OFFICE Gerhard Frenkel, Rudersdorf, near Berlin, Germany N Drawing. Application July 19, 1938, Serial No. 220,154. In Germany July 19, 1937 12 Claims.

The present invention relates to a sintered binding agent of the Portland cement type, and process for manufacturing same. For the purpose of explaining the invention and appreciating the technical advantages connected therewith, it may be pointed out that, when manufacturing the raw mixture of Portland cement or cement in general, the quantity of the ingredients is given in proportion of weights.

1 The four main ingredients of Portland cement consist, as is well known, of lime (CaO), silica (SiOz), alumina (A1203), and ferric oxide (F6203). For the purpose of judging the kind of mixture, the proportion of the content of lime to the sum of the contents of silica, alumina and ferric oxide CaO SiO2+Al203 +F6203 has been called hydraulic modulus. Later on, the designation silicate modulus has been introduced for the proportion of silica to the total quantity of alumina and ferric oxide S102 A1202 +F203 the designation alumina modulus has been introduced. From the proportion of mixture of the raw stuffs on the basis of certain numerical values for these moduli, the properties of the cement manufactured from the raw mixture will result.

The modern method of building with concrete requires cements, which, in addition to high tensile, compressive and transverse strengths, both in the beginning of the hardening process and its later course, show a good plasticity in mixing, a low demand for water, a development of heat, which is as low as possible, when setting, a low modulus of elasticity and a tendency to shrinkage, which is as low as possible.

In order to comply with these requirements, 50; the process formerly recommended by Ferrari, an

alumina A1 O ferric oxide Fe O 25 silica SiO alumina-l-ferric oxide Al O +Fe O between 1.10 and 1.75 shall preferably lie at 1.40, whilst the alumina modulus, i. e. the proportion alumina Al O ferric oxide Fe O between 0.90 and 0.45 shall preferably lie at 0.64. Consequently, this process is distinguished from the Ferrari process merely in so far as in the former process, the silicate modulus is artificially reduced to a considerable extent.

However, cements of the combination recom- 40 mended have drawbacks both in the manufacture and in the working, thereby making the application of the process questionable.

In the first place, difiiculties are experienced when burning the cement, the material to be burnt having a strong tendency to melt, thereby sticking fast in the kiln. The troubles, caused thereby, will occur all the more with the reduc-v tion of the modulus within the limits resulting from the proposal made. Owing to the melting 5o process, which can practically never be avoided in these mixtures, a very dense cement clinker is produced, the grinding of which offers considerable difiiculties. An additional disadvantage in the manufacture results from the high costs of raw materials connected with the considerable additions of ferric oxide, inasmuch as, for the purpose of obtaining an alumina modulus of 0.64 or a still lower modulus, very pure iron ores have to be added, which are now scarcely at disposal for this purpose.

In working these cements, the alumina modulus of which lies at 0.64 or below, they show a comparatively sluggish initial hardening, so that they can no longer be regarded as highly valuable cements.

The inventor has found that all these drawbacks can be obviated by combining the cement in such a manner that its silicate modulus lies between 1.75 and 2.00, preferably at 1.90, and that its alumina modulus lies between 0.70 and 0.90, preferably at 0.80. Various cements of this composition have but little tendency to melt, so that they guarantee a perfect operation of the kiln and the burning of a well sintered but still unmolten and extraordinarily brittle clinker, which can, therefore, be easily ground. Owing to the intended very slight increase of the alumina modulus over and above the equivalency proportion of 0.64, the presence of small quantities of free aluminate ions is also guaranteed, which will strongly influence the hardening process, without, however, having an iIljllllOllS effect on the shrinking property of the cement in view of their weak concentration.

The present invention has at the same time for its object to produce a raw mixture of cement with the characteristic feature that only a small number of additional materials are required. This offers the technical and economical advantage that the working methods for the mixing process are greatly simplified.

It has not only been possible to fix this process in this manner in a theoretical way, but, in view of the present scarcity of iron, to find also a suitable method for carrying out the process on a large scale, in connection with which the selection of the lime stone on the one hand and that of the iron oxide carrier is of considerable importance.

As regards the lime carrier, according to the invention a sort of lime stone is preferably used, which, in addition to carbonate of lime, contains also silica of a quantity of about 10% and sesquioxide in quantities of about 35%. This sort of lime stone may be called briefly wavelime. In accordance with the invention, instead of the normal ferric oxide component, a red iron stone is used, which, besides its comparatively low content of ferric oxide, viz. about 32-40%, still contains so much silica and alumina that, when mixing it with the wave-lime and under certain circumstances by adding sand-flour of about 2% of the total mixture, guarantees the combination of the raw mixture for the most desirable properties of the binding medium to be produced. This will have the effect that the alumina modulus and the silicate modulus conforms to the limits mentioned. By this means, the most important idea of the invention, which has already been more clearly described, is realized, so that a cement is produced, whose main quantity of alumina is bound in the form of tetracalcium alumino-ferrite, but which,and this is the most important pointcontains a low percentage of free aluminate ions (originating from tricalcium aluminate), whereby the hardening process is strongly influenced, without, however appreciably increasing the shrinking property of the cement. Furthermore, the content of silica in such a cement is such that the clinker can be burned free from any trouble and that it can be easily ground.

As regards the ferric oxide carrier as an additional material, a strong gangue-containing German iron ore has been found, which contains all hydraulic factors-in a quantity necessary for determining the raw fiour, besides showing such a low content of ferric oxide that, at present, it does not come into consideration for the metallurgical treatment of iron. On the contrary, large quantities of ore, containing but little iron, had to be moved within the last few years, for the purpose of working ore which is rich in iron and ready for smelting, and which had to be thrown on the dump, but which can now be utilized commercially for the manufacture of the new cement. By this means, the working of iron ore involved is not only rendered more economical, but new possibilities are offered in the future for extracting ore deposits, the working of which has hitherto not been profitable.

The content of silica necessary for convenient grinding, i. e. for a brittle clinker, might also be produced artificially, for instance by adding a different iron ore containing a still larger quantity of sand flour. By using red iron ore of the kind described, containing but little ferric oxide, we have the advantage-which must not be underestimated-that in that case the silica is added either wholly or for the most part to the raw mixture in a form made available by nature in an abundant quantity, which has a great influence on the combustibility and properties of the burnt cement and cannot be attained by artificial mixture.

As a matter of course, the advantages described above, resulting from the use of a red iron ore containing but little oxide, will act in the same manner, if no lime marl of the kind described (wave-lime) is at disposal as an initial material, but if lime stone and clay is used as an initial material of the raw mixture, as is the case in most cement factories.

The wave-lime, described above, has the advantage that the quantities of lime, silica and sesquioxide, attainable by artificial mixture of lime stone with clay in other refractories, are already supplied by a single natural material. When using wave lime and also when using lime stone and clay, the same advantage is attained by an addition of the above mentioned red iron ore which contains but little oxide, in so far as no sand flour at all or only a very small addition of sand flour (not exceeding 2%), or of other materials containing silica is necessary, in order to obtain the desired combination of the raw mixture with regard to the silica, while, by using any other ferric oxide carrier (for instance a different ore or purple ore), the addition of considerable quantities of one or several additional raw materials, such as sand, clay, slag or other materials containing silica is indispensable, since these iron carriers are not so favourably combined by nature.

With a cement of the new combination, it is in the first place possible, to accentuate the low shrinking property, to a considerable extent. The following table, in which the testing results,

obtained with the new cement are compared with those of some sorts of Portland cements or road I claim: making cements, may serve as an illustration. 1. Method of forming a sintered binding agent Transverse strength Compressive strength plastic Shrinkage I (Kg/cm!) (Kg/0111 (Mm/m.) I 7 Age (days) 1 a 7 23* 2s 1 3 7 28* 28" 2s 56 9o Cement according to the invention 24 53 67 86 74 99 293 431 559 622 0.22 0.41 0.49 Road making cement No.1.... 15 38 51 68 83 61 183 305 437 456 0. 60 0.61 0,62 Road making cement No. 2.... 18 41 55 76 92 62 188 289 479 534 0.56 0. 68 o. 70 10 Portland cementNo. 1... e 23 37 59 63 21 92 161 350 35s 0. 50 0.80 0.83 Portland cementNo. 14 33 i9 64 74 46 148 251 451 47s 0. 44 0. 79 0. st

- Water bed. Unit bed.

In the table given above, the figures for transwith a carbonate of lime content of the Portland verse strength and plastic compressive strength cement type characterized by high strength and 15 have also been included, from which it can be w Shrinkage, Which Comprises preparing a aw seen that, in cc d n ith th i ti th mixture containing limestone and iron ore, said cement issuperior to, the sorts of Portland cemiXtuIe hoVing as Components Silica, u ments and ad making t which ha and iron oxide adjusted to a silicate modulus bebeen compared. Its values attain about those of tween and 2-00, the content of alumina b i cements of high and specially high value. It has adjusted to an um a modulus between 0.70 hitherto not been possible in any case to obtain and 0-90, and sintering Said tu e. such a low tendency to shrinkage simultaneously Method of forming a sintered binding agent such a transverse trength and com a carbonate Of content Of the Portland pressive strength so that, in case of t cement type characterized by high strength and called cements of high and especially high low Shrinkage, wh ch comprises Preparing a aw value, either a considerable tendency to shrinkmixture Containing limestone and iron a d age had to be admitted, or the main value was mixture having as components silica, m tt t a moderate tendency to Shrinkage, and iron oxide adjusted to a silicate modulus of so that one had to be content with comparatively approximately the C te t o a u a below figures relating to the strength (road making adjusted to an alumina modulus of DP t imately 0.80, and sintering said mixture.

Owing to ery low shrinkage property in 3. Method of forming a, sintered binding agent connection with high figures relating to strength, with carbonate of lime content of the P a d the new cement is more fit for covering concrete Cement type Characterized by high strength and roads and as a binding agent for the concrete 10W Shrinkage, Which Comprises preparing a w goods industry t ,11 other cements mixture of a lime carrier and an iron oxide car- AS an additional ery important improvement, rier, the lime carrier being a limestone which, in the high plasticity of the newv cement may be addition to carbonate of lime, contains 811% mentioned, which, in connection with a very low of Silica and of SesqllioXides, the iron oxide 40 demand for water, enables the manufacture of a carrier being a red iron Ore which, in addition comparatively dry and well Working pliable conto a low content of about iron oXide, Crete mixture contains 40-50% silica, 3-5% alumina, and 2-5% Owing t t exclusion of t calcium 1 lime, the proportions being such that the silicate minates, the new cement shows a very low demodulus of the raw mixture is adjusted to velopment of h t i setting, so t t in tween 1.75 and 2.00 and the alumina modulus is nection with the high figures relating to strength adjusted to between and 0-90, d Sinterihg and its low tendency to shrinkage, it represaid mixturesents a first class binding agent for wholesale con- Method of forming a sintered b d a ent Crete (Works of fortification flood-dikes t with a carbonate of lime content of the Portland Finally, the new cementlikewise owing to the cement y characterized y high strength and absence of larger quantities of calcium alumi- 10W Shrinkage, Which comprises p p i natespossesses a far greater resisting force mixture of a lime Carrier and an iron oxide agaihgt tt of sulphafic ground Water than rier, the lime carrier being a limestone which, in all other common sorts of Portland cement. addition to Carbonate of lime, o a 811% of In cooperation with all the advantages men- Silica and of sesquioxides, e n oxide tioned above, the new cement, therefore, reprecarrier being 31 red iron ore Which, in d o gents ahideag standard binding agen1; to a low content of about 32-40% iron oxide,

Finally, the following example will show in contains a um na. and 2.5% what manner a cement within the meaning of the lime, the Proportions being Such that the 5111- present invention is composed, viz. a cement, Cate modulus of the raw mixture is j d o which shows the most favourable combination approximately and t alumina du us is both for the silicate modulus and the alumina adjusted to approximately 0-80, and sintering said modulus, and with which the lime standard can mixturebe brought up to roughly 00 5. Method of forming a sintered binding agent Silica 1910 with a carbonate of lime content of the Portland Alumina 4A7 cement type characterized by high strength and Ferric Oxide 558 low shrinkage, which comprises preparin a raw Lime 6223 mixture of a limestone which, in addition to car- Magnesie 290 bonate of lime, contains 811% of silica and 34% Gypsum 5,00 f sesquioxides, red iron ore, and other silica con- Loss due to glowing, and insoluble ubtaining material, so proportioned as to adjust the stances 0.67 silicate modulus of the raw mixture to between Alumina modulus 0.80 1.75 and 2.00, and the alumina modulus to be- Silicate modulus 1.90 .tween 0.70 and 0.90, and sintering said mixture.

6. Method of forming a sintered binding agent with a carbonate of lime content of the Portland cement type characterized by high strength and low shrinkage, which comprises preparing a raw mixture of a limestone which, in addition to carbonate of lime, contains 8-11% of silica and 3-6% of sesquioxides, red iron ore, and other silica containing material, so proportioned as to adjust the silicate modulus of the raw mixture to approximately 1.90, and the alumina modulus to approximately 0.80, and sintering said mixture.

7. The method described in claim 1, wherein the sintered mixture is ground with an addition of 4-6% of gypsum.

8. The method described in claim 2, wherein the sintered mixture is ground with an addition of 4-6% of ypsum.

9. A sintered binding agent of the Portland cement type, the silicate modulus of which lies between 1.75 and 2.00, and the alumina modulus of which lies between 0.70 and 0.90.

10. A sintered binding agent of the Portland cement type, the silicate modulus of which is approximately 1.90, and the alumina modulus of which is approximately 0.80.

11. A binding agent of the Portland cement type, comprising a ground mixture of 4-6% gypsum with a clinker having a silicate modulus Which lies between 1.75 and 2.00, and an alumina modulus which lies between 0.70 and 0.90.

12. A binding agent of the Portland cement type, comprising a ground mixture of 443% gypsum with a clinker having a silicate modulus of approximately 1.90, and an alumina modulus of approximately 0.80.

GERHARD FRENKEL. 

